Precision spectroscopic measurements can reveal a wealth of information about our surrounding world. With laser spectroscopy, one can perform measurements in the atmosphere that expose physical, chemical, and geological processes on Earth, detect trace amounts of hazardous gases, carry out medical breath analysis and even discover traces of life in the outer planets. Conventional methods of spectroscopy could either be ultrasensitive but limited in their range of molecules to be detected (e.g., narrow-bandwidth lasers), or broad-range but not sensitive enough (e.g., Fourier transform infrared spectrometers).
Precision frequency combs (that is a sequence of sharp peaks on the frequency scale) generated by mode-locked lasers in the visible, UV and near-infrared wavelength region have led to revolutionary advances in spectroscopy. Spectroscopic methods of detection based on frequency combs at longer wavelengths, which is near molecular vibrational ‘fingerprint’ resonances, can be exceedingly advantageous in terms of both high sensitivity and specificity.
Infrastructure protection against a terrorist-based weapons-of-mass-destruction (WMD) attack and cargo screening for possible hazards are among the many applications that provide examples of recent security challenges. For example, in the event of a hazardous agent's release, timely decision-making depends on sensitivity, reliability, and response time of an early warning system in place. Cargo screening at airports and seaports requires a standoff instrument for rapid, high-throughput scanning or real-time imaging of large surface areas that enhances security without delaying the flow of goods and passengers.
Precision frequency combs generated by mode-locked crystalline and fiber lasers can be useful for providing advances in spectroscopic detection of trace gases: several research groups have recently demonstrated high detection sensitivity, ability to identify and distinguish simultaneously a number of analytes and real-time information processing.